Thermionic converters



Sept. 27, 1966 R. L. LAING ETAL THERMIONIC CONVERTERS 4 Sheets-Sheet 1Filed June e, 1965 Sept. 27, 1966 R. L. LAING ETAL THERMIONIC CONVERTERSFiled lJun@ e, 1965 4 Sheets-Sheet 2 L, l l J wwf N www i m r. mi@ A TSept 27, 1966 R. L. LAING ETAL THERMIONIC CONVERTERS Filed June 8, 19654 Sheets-Sheet 3 Sept. 27, 1966 R. l.. LAlNG ETAL 3,275,923

THERMIONIC CONVERTEBS Filed June 8, 1965 4 Sheets-Sheet 4.

MAXIMUM POWER POINT 165 SPACE CHG. LIMITED CURRENT INVENTORS 20322? LLAING,

622m J2 Fuws'zz MAX. POSSIBLE COLLECTOR CURRENT I I l 25 5o 75 loo BYMAX. POSSIBLE COLLECTOR VOLTAGE THERMIONIC GENERATOR COLLECTOR VOLTAGEVS LOAD CURRENT United States Patent Gfiice 3,275,923- Patented Sept.27, 1966 3,275,923 THERMIONIC CONVERTERS Robert L. Laing, 3527 AquilaAve. S., St. Louis Park, Minn., and Carol D. Feemster, 444 W. DuarteRoad, Apt. E-3, Arcadia, Calif.

Filed June 8, 1965, Ser. No. 462,384 19 Claims. (Cl. 322-2) Thisapplication is a continuation-impart of 'our prior application, SerialNo. 222,426, filed September l0, 1962, now abandoned.

The present invention relates to thermionic converters in Iwhich heatenergy is converted into electrical energy, the heat energy beingapplied to thermionic 'cathodes or electron emissive elements. Theelectrons emitted are collected on a second surface, termed a collector,producing a negative voltage on this second surface. If a load isconnected between the collector and the thermionic cathode, an electroncurrent will flow through the load producing usable electrical energy.

The present invention is specifically concerned with an improved form ofsuch ya thermionic converter. It is obvious that if heat is applied to athermionic cathode, there is some tendency for the heat to betransferred to the collector with the resultant loss of efficiency,particularly if the collector is in close proximity to the cathode, asis the common practice with previous thermionic converters. This heattransfer may occur by reason of radiation or by conduction through anyplasma present in the tube. One of the objects of our invention is toreduce su-ch heat transfer. Broadly, this is accomplished by employingan accelerating anode between the thermionic cathode and the collectorfor the purpose of drawing the electrons a relatively long distance awayfrom the cathode, thus making it possible to have a substantial spacingbetween the collector and the electron emissive surface. Such increasein spacing tends to reduce any heat loss by reason of radiation from thethermionic emissive surface to the collector.

Because yof the presence of the accelerating anode in our device, thespace charge adjacent to the electron emissive surface is reduced andtherefore the device is maintained at a high vacuum. Hence, Iit becomesunnecessary to use an ionizing gas such as is often used in presentthermionic converters. Such ionizing gas, `in many cases, may be quitecorrosive, ce-sium being one example. The elimination of the ionizinggas not only eliminates the corrosive effect but also reduces the heatloss through the plasma.

It is also an object of your invention to provide a thermionic converterin which the electrons travel in a generally linear path in movingbetween the electron emissive surface and the 'collector surface. It hasbeen proposed inthe prior art to use thermionic converters of thecrossed field type in which there is magnetic field which is parallel tothe surface of the electron emissive surface and which bends theelectron projectory into a cycloidal or trochoidal path. In ourconverter, an accelerating anode has an aperture therethrough, throughwhich the beam of electrons passes. Where a magnetic field is employed,this magnetic field is employed for focusing purposes in- -stead of fordeflecting the beam.

A further very important feature of our invention is the fact that ahollow collect-or is preferably employed. This hollow collector iscomparable to the hollow collector of a Van de Graaff generator. As hasbeen demonstrated in connection with Van de Graaff generators, theinterior of such a hollow collector is at a substantially Iuniformpotential at all points therein. The electrons injected into t-he hollowcollector will go to the surface of the collector due to their mutualrepulsion. This has the advantage that the electrons ejected into thecollector tend to reach the surface Iof the collector so a-s to becollected in the load circuit, rather than being repelled away from thecollector surface due to the negative potential thereof. Thus the usualpower output is greatly increased. This also makes possible theattainment of much higher collect-or potentials than has hitherto beenpossible.

Because of the fact that the need for an ionizing gas is eliminated `anddue to the much greater spacing between the electron emissive surfaceand the collector, it becomes unnecessary to use any means for coolingthe collector as has been done in connection with previous thermionicconverters. This further increases the efiiciency of our device.

Referring to the drawings,

FIGURE 1 is a sectional view of one form of our thermionic converter inwhich an electromagnet is employed to produce a parallel electron flowinto a hollow collector and in which the heat source of the cathode is aflame;

FIGURE 2 is a partial view showing a modification of the thermionicconverter of FIGURE 1;

FIGURE 3 is a form of a thermionic converter employing an electron gunin combination with a permanent focusing magnet for `directing the beamof electrons into a hollow collector, the disposition of the electrodesbeing similar to that of a Pierce type gun `and again with the heatsource of the cathode being a fiame;

FIGURE 4 is a sectional view of another form of our thermionic converterin which, for :purposes of illustration, the electron emissive surfaceis heated by a coil through which hot gases flow;

FIGURE 5 is a view similar t-o that of FIGURE 4, but in which thesection is taken at right angles to the plane of section of FIGURE 4;

FIGURE 6 is a view yof a further modification of our gun in which theelectron emissive surface is also shown for purposes of illustration asbeing heated by radioactive material;

FIGURE 7 is a partial view of a modification of the collector in whichpointed projections within the collector .alter the voltage gradientwithin the collector; and

FIGURE 8 is a chart showing the relationship between the current throughthe load and the collector voltage as the load resistance i-s increased.

Referring specifically to FIGURE 1, our thermionic converter is housedwithin an envelope including a cylindrical neck portion 11 and a hollowspherical collector port-ion 12. The neck portion 11 houses the elementsof the electron gun including a cathode assembly having a thermionicemissive cathode surface 13, a control grid 14, an accelerating anode15, and an electrostatic electrode 16. An electromagnet 17 surrounds theneck portion 11 and serves to concentrate the electron beam as will bepresently described. A collector 12 is shown in FIGURE l, as comprisingan outer portion 19 of glass or similar nonconductive material, to theinterior of which is applied a coating 20 of suitable conductivematerial such as metal. The collector portion 12 and neck portion 11 maybe either integral with each other, as shown, or joined to each other byany conventional method providing a vacuum-tight seal therebetween.

Referring more specifically to the elements of the gun, the cathodeassembly is in the form of an inverted cylindrical cup 22. The cathodemay be formed of nickel with the upper electron emissive surface 13coated with equimolar proportions of barium and strontium oxides. It is,of course, understood that any of various other electron emissivesurfaces may be employed. The cylindrical cup member 22 of the cathode13 is supported in -a disc 23 of ceramic or other suitable material andsuitable vacuum-tight seals are provided between the cylinder 22, thedisc 23, and the neck portion 11 of our converter. The entire assemblageincluding the neck portion 11 yand the collector are evacuated to avacuum of -10 to 10-6 torr. This p-ressure may be held by means of apump or -by the use of a suitable getter within the envelope.

The electron emissive surface 13, which in the particular example shownmay have a diameter from 1 to 5 centimeters, is shown as heated by aiiame 25 issuing from a burner 26. It is to be understood that the flame25 represents a source of heat which is to be converted into electricalenergy. Any of various sources of such heat may be employed and in someof the other modifications, we have shown other sources of heat. It isto be understood that the invention is not limited to any particularsource of heat, and that in connection with any of the modifications,different sources of heat may be employed.

The control grid 14, in the particular example illustrated, is locatedabout .060E inch above the cathode surface 13. This control grid has anaperture 27 therethrough, which aperture may have a diameter of from .5to 2.5 centimeters. The aperture 27 is located concentrically withrespect to the beam 28 of electrons emitted by the cathode surface 13.

The accelerating anode is shown in the form of a cylinder having aninside diameter slightly less than the aperture 27 of the control grid.This accelerating anode may be located from about one-fourth to twoinches above the control grid 14.

The electrostatic electrode 16 acts to modify the field between theanode and collector to reduce the tendency of the electrons to return tothe anode and thus increases electron flow into the collector 12. Theelectrode 16 also aids in focusing the electron beam. This electrode 16may be located concentrically around the accelerating anode, 4as shown,or about .080 inch above it. As shown, the electrostatic electrode 16surrounds the upper end of anode 15, being insulated therefrom by anannular memfber 30' of ceramic or other suitable material. Theelectrostatic electrode 16, located slightly above the anode 15, mayhave an interior diameter only slightly larger than the interiordiameter of the anode 15.

The control grid 14, the anode 15 and the electrostatic electrode 16 maybe made of molybdenum, 304r stainless steel or any other suitable highmelting point, low gas emitting conductive material. The materialforming the coating may be copper, gold or other similar material havingrelatively low secondary emission.

During the construction of the tube, the entire assembly is baked at 300to 450 C. while being vacuum pumped to drive the gases out of thevarious parts. The cathodes may be initially coated with barium andstrontium carbonatos in a nitrocellulose binder and the cathode isheated to about ll50 C. to convert these to the barium and strontiumoxides referred to previously. While not shown, the entire envelope maybe immersed in transformer oil to prevent external arcing of theelectrode feed-throughs and to remove heat from any local hot areas.

Referring speciiically to the electrical connections, the

cathode assembly 22 is connected to a suitable ground connection 32.Connected between the control grid 14 and the cathode assembly 22 is asuitable source 33 of control vol-tage wh-ich is connected across aresistor 34, which in turn is connected between the cathode 13 and theaccelerating grid 14. The source 33 of control voltage may provide anyof various types of voltages such as an alternating voltage to modulatethe beam 28 to produce an alternating component lin the output volt-`age. Thus, the control voltage may vary, for example, between ninetyvolts negative and thirty volts positive so as to turn the beam ofelectrons 28 on and off alternately. It is to be understood, however,the control voltage may be merely a voltage of any desired magnitude 4to introduce a control effect in accordance with a desired condition. Itis to be understood, of course, that the control voltage is notnecessary in many applications of our device.

The anode 15 has the function of pulling the electrons away from thecathode and has a relatively high voltage applied thereto. In a typicalcase, the voltage applied to the anode 15 may be from 5 to 10 kilovolts.While it is to be understood that any suitable source of voltage capableof generating voltages of this magnitude may be employed between theanode 15 and the cathode, we have shown a rbattery 35 for this purpose.It is understood, however, that the battery is intended to be merelyillustrative of a suitable power supply.

The electrostatic electrode 16 is maintained at a po tential somewhatnegative with respect to the cathode. This potential should preferablybe selected to provide for the maximum ratio of collector current andanode current. For purposes of illustration, we have shown a battery 36for applying this potential.

A further battery 37 is shown as connected across the terminals of theelectromagnet winding 17. This battery is selected to have a voltageoutput of a magnitude to produce a current to the electromagnet windingsufficient to produce the desired focusing of the beam 28. A field of600 to 1200 gauss is typical of that employed. The magnitude of thisvoltage, of course, depends upon the nature of the electromagnet 17 The-overall operation of our thermionic converter, as `shown in FIGURE 1,Will now be described. The source of heat to be converted intoelectricity, such as fla-me 25, is effective to heat the electronemissive surface of cathode 13 thus causing a stream of e'lectrons toissue therefrom. The stream of electrons is focused by the electromagnet1-7 so as to cause it to pass through the opening 27 in grid 14 Wherethe stream is affected by the voltage produced by the source 33 ofcontrol voltage where such a control voltage is employed. Where it isnot employed, resistor 34 provides a grid return to maintain 4the grid14 :at a desired voltage. The beam 28 is held in a concen- -tratedstream by the magnetic field produced by electro'- magnet `17 so as tocause it to pass through the opening in accelerating electrode 15 towhich the beam is accelerated as the result of thevrelatively highvo'l-tage applied to .the accelerating anode 15. By sufficientlyconcentrating the beam 28 of electrons and by applying a sufficientlyhigh voltage to anode [15, the acceleration of the electrons will besufficiently high to cause substantially `all of them to pass throughthe anode 15 so as to cause negligible drain on the anode power source,shown as battery 35. lDue to the electrostatic electrode 16, which aspreviously explained, is maintained ata negative potential with respectto the cathode, the iield between the anode and collector is modified soas t-o reduce the tendency of the electrons to return to the anode 15.If it were not for this electrode, there would be a high positive fieldin this region and the electrons would have difficulty in passingthrough this field. Partially because of this electrode 16, most of theelectrons tend to enter the collector. The potential at which electrodeI16 is maintained is, as previously pointed out, selected 4to providethe maximum ratio of collector current to anode current.

When the electrons enter the collector 12, they are no longer under theeffect of the field focusing electromagnet I17, and are free to moveapart due to their mutual repulsion. Since the potential within thespherical collector l1-2 is substantially equal throughout, theelectrons will be moved substantially uniformly to the interiorconductive coating 20 of the collector. This movement of the electronstakes place despite the negative potential on the interior conductivecoating for several reasons. In the firs-t place, as pointed out above,the electrons, once they enter the ho'llow collector 12, are mutuallyrepelled from each other. They hence tend .to force themselvesapartcausing them to accelerate and thus acquiring additional velocity. Thisadditional velocity enables the electrons to move into engagement withthe conductive surface 20 vdespite its negative potential. Furthermore,due to the presence of the load circuit, including load 38 (presently tobe referred to), the electrons are removed from the collector throu-ghthe load. The load 38 is connected between the conductive coating of thecollector and the cathode to form a utilization circuit so that, asmentioned above, as the electrons collect -on the conductive surface 20of the cathode 12, they flow through this utilization circuit back tothe cathode. This current flow through load 38 results in a usefulelectrical output. Due to the construction of our device, verysubstantial voltages may be produced between the collector 12 and thecathode 13. In actual experimental work, voltages as high as minus 18volts have Ibeen obtained on the collector 12 when the load 38 wasconnected, and voltages as high as minus 180` volts when the loadcircuit was disconnected. It is obviously very desirable to have anappreciable vol-tage between the collector 12 and the cathode |13 sincesuch voltages are of greater utility than the relatively low voltages ofpresent thermionic converters.

Modification of FIGURE 2 In the modifie-ation of FIGURE 2, thethermionic converter is basically the same as that of FIGURE l exceptfor the Iaddition of two pre-accelerator electrodes.

In FIGURE 2, only the gun portion of the thermionic converter has beenshown since the collector is exactly the same as in FIGURE 1. Except forthe pre-accelerator electrodes, the same reference characters have beenapplied as in FIGURE 1 to facilitate a comparison of the two figures.The two pre-accelerator electrodes are designated 4by the referencenumerals 401 and 41. These electrodes are spaced be-tween the lgrid 14.and the accelerator anode 15. Electrode 40 is provided with an aperture42 and electrode 41 with an aperture 43. These apertures 42 and 43 aresubstantially the same in diameter as the aperture 27 of grid 14 and arecoaxial with respect to .the stream 28 of electrons. Electrodes 40 and41 are connected to taps 44 and 45 of the voltage source 35 for applyinga voltage to the accelerator anode '15. The taps 44 and 45 are soselected that the voltage between the cathode 13 and the pre-acceleratorelectrode 40 is approximately equal to that between pre-acceleratorelectrodes 40 and 41 and between pre-accelerator electrode 41 and yanode'15.

The effect of the pre-accelerator electrodes 40` and 41 is to cause agradual increase in acceleration of the bea-m of elec-trous 28 so thatthe stream of electrons is reaching a more parallel path when it passesthrough the opening in accelerating anode 15.

Modification of FIGURE 3 In the thermionic converter of FIGURE 3, wehave employed a gun construction in which the electrodes are arranged ina manner similar to that in the Pierce type gun. The inverted cup-shapedcathode assembly designated in this ligure by the reference numeral 504is provided with an electron emissive surface or layer 51 which, by wayof example, may be sintered tungsten impregnated with lbarium andstrontium oxide, commonly referred to as a Phillips or L-type cathode.Any of various other common electron emissive surfaces or layers may beemployed. As shown in the drawing, the cathode is flat on top but thiscathode may have a concave spherical shape or other concave shapes, theemissive surface having a diameter from one to ten centimeters. Aspointed out, the emissive surface 51 is shown as iiat in FIGURE 3 and inthis case, it is surrounded by a focusing electrode 53 suitablyinsulated by an insulating spacer 52 from the cathode 50. The focusingelectrode is conical and the surfaces thereof form an angle of about67.5 with respect to the beam axis. If the cathode 51 has a `sphericalsurface, the focusing electrode is` a continuation of the cir- 6cumference of the spherical surface. The focusing electrode 53 may tbeelectrically connected with the cathode `50 and at the same potential asthe cathode. On the other hand, where it is insulated therefrom, asshown, it may be maintained at a somewhat negative potential with re--spect to the cathode by a suitable source of .power supply such asbattery 54. The lfocusing electrode 53 is shown as sealed to the tubularneck 55 of the gun, this seal being of any well known type whichmaintains a vacuum type seal between the focusing electrode 53 and theneck 55. The neck 55 is of suitable insulating material such as glass orceramic. Located above the cathode is an accelerating anode 56 which hasa function similar to that of accelerating anode 15 of the species ofFIGURES 1 Iand 2. In one particular embodiment of our invention, theaccelerating anode may be located at a distance of from .060 to .500inch above the cathode. This accelerating anode is 4shown as having anaperture 57 concentric to the beam of electrons, which aperture isslightly less in the diameter than the diameter of the cathode. The`anode 56 is maintained by a suitable source of voltage 59 -at apotential which may range from about 1000 to 10,000 volts. Secured tothe tubular neck 55 of the gun is a collector 60. In this particularcase, the collector `is shown as being formed of metal, it beingunderstood that in any of the embodiments it is possible to employeither a metal collector such as collector 60 or an envelope ofinsulating material such as envelope 19 having a conductive coating 20therein, as illustrated in connection with FIGURE 1. The collector 60`has an aperture 6\1 therein, which `is slightly larger than the aperture57 of the anode 56. In this particular embodiment, the aperture 611 isin a re-entrant frusto-conical flange 62 wlhich acts to .trap theelectrons after they have passed through the collector aperture 61.

In FIGURE 3, we have shown a permanent magnet 63 as being employed tomagnetically focus the beam. The magnet 63 is shown in section. Thismagnet comprises two generally U-shaped portions at their upper andlower extremities. At its upper extremity, the legs 64 abut along theline 65. The legs 64 are shown in dotted lines in the yligure and jointhe main portions of the magnets 63 along a diagonal line 66 conforminggenerally to the contour of the collector 60. It is to be understoodthat there are two such similar legs 64 for each ha'lf of the magnet andthat these legs surround the collector 60. At their lower end, eachsection of the magnet 63 is provided with a pair of legs 67 which abutalong the line 68 and which closely surround the neck portion 55 of thegun. The effect -of the ma-gnet 63 is to focus the beam of electron-sand to closely confine the same so that it passes through the aperture57 of the anode 56 vand the opening 6:1 of Ithe collector 60 withoutappreciable spreading of the beam and thus without any substantiallosses due to anode current. It is to be understood that in place of ayoke type magnet such .as magnet 63, it is possible to employ a hollowcylindrical magnet with a magnetic field direction parallel to the axisof the electron beam. It is also contemplated that the electron 'beamcould be foculsed by electrostatic fields only, in which case no magnetneed -be employed.

The collector 60 which may be 1 to 10 inches in diameter, in theparticular embodiment being discussed, is sealed in a suitable manner tothe neck portion 55 to form a vacuum type seal therewith. The entireunit including collector 60 and neck 55 is highly evacuated as in thecase of the thermionic converter of FIGURES 1 and 2.

The cathode 50 is shown as bein-g heated by the flame 70 of a burner 71,this being merely one particular way of heating the cathode as waspointed out above.

In connection with the modification of FIGURE 3, a suitable load 7B isconnected between the collector 60l and aground connection 74 which inturn is connected to the cathode 50.

The operation of the gun of FIGURE 3, as far as its broad function ofconverting thermal energy to electrical energy is generally similar tothat of the modications of FIGURES 1 and 2. This beam of electronsemitted from cathode 51 is focused by the focusing electrode 53 and bythe magnet 63 so that the beam of electr-ons enters the interior ofhollow collector 60 in which the electrons are repelled from oneanother` to engage the surface of the collector 60. Due to the sphericalnature of the collector, these electrons are repelled to the surface ofcollector 60, despite the high negative charge produced thereon, andflow through the load device 73 back to the cathode 50. In this way, thethermal energy of the llame 70 is converted into electrical energy.

Modification of FIGURES 4 and 5 The thermionic converter of FIGURES 4and 5 is similar in electrode disposition to the so-called Hiel gun.This gun is provided with a concave cathode member 76 provided with asuitable electr-on emissive coating on the upper face thereof. Anelectrostatic focusing electrode 77 has an interior spherically concavesurface which forms `a continuation of the concave electron emissivesurface of cathode 76. Electrostatic focusing electrode 77 is sealed tothe cathode 76 by an insulating annular ring 78 which Iforms an inwardlyextending collar of an insulating sleeve 79. The collar 78 is sealed tothe cathode 76 and the electrostatic focusing electrode 77 in a suitablevacuum type manner. The sleeve 79 for-ms a chamber around the undersurface of cathode 76 and this cathode may be suitably heated in anydesired manner. We have showna coil 80 having an inlet 81 and an outlety82 and a plurality of coil turns 83 through which a hot fluid may becirculated. For example, this may be hot exhaust gas which it is desiredto convert into useful electrical energy. Instead of employing a coil80, the lower end of the cylindrical chamber 79 may be sealed and thehot gas may ybe simply passed through this chamber coming -in contactwith the under surface of cathode 76. It is, of course, to be understoodthat any other means may be employed for heating the cathode 76 by asuitable source of heat which it is desired to convert into electricalenergy Located above the electrostatic electrode 77 is an anode 90having an interior spherical surface which is shaped to constitute acontinuation of the spherical surface of electrostatic electrode 77. Theanode 90 is sealed to the electrostatic electr-ode 77 by an annularmember 91 of dielectric material. Interposed between the anode 90 and aspherical collector 92 is an insulating ring 93 which is curved so as toform a curved entrance throat to the collector 92. It is understood, ofcourse, that the ring 93 of dielectric material is suitably sealed in avacuum type'manner to the accelerating anode 90 yand to the collector92. We have shown sweep coils 94 and 95 as disposed at right angles tothe axis of the beam of electrons. These sweep coils are connected to asuitable source of alternating voltage 96.

A voltage which may vary from zero to 50 volts negative is appliedbetween the electrostatic electrode 77 and the cathode 76 by a suitablesource of voltage 98. A relatively high voltage which may range from10,000 to 100,000 volts positive is maintained between the anode 90 andthe cathode 76 by a suitable source of voltage 99.

In the operation of the modification of FIGURES 4 and 5, the electronbeam emitted lby the electron emis` sive surface of anode 76 is causedto converge due to the concave spherical surface of thecathode 76 sothat it passes through the anode 90 as a relatively narrow beam. Thefocusing of this beam is aided by the electrostatic focusing electrode77 which is maintained lat a negative potential for this purpose. Uponentering the collector 92, the electrons are mutually repelled to engagethe interior conducting surface of the collector 92. The electrons canthen pass from the collector 92 through 8 a suitable load device back tothe cathode 76, thus causing a current ilow through the load 100.

Referring for the moment to FIGURE 5, it will be noted that the coils 94and 95 (only coil 95 being shown in FIGURE 5) and the polarity of thecurrent therethrough are in such a direction that the magnetic fieldproduced thereby tends to cause the electr-ons to be dellected to oneside of the collector 92. Due to the alternating current applied toelectron coils 94 and 95, this effect is periodically reversed so thatthe beam of electrons yare swept from side to side within the hollowcollector 92 to aid `in dispersing the electrons throughout the interiorsurface of collector 92. Instead of coils such as coils 94 and 95,electrostatic deflection plates can be similarily employed and in thiscase an alternating source of voltage will be applied to these plates.The feature of the deflection means, such as that provided by coils 94and 95, is an optional feature which may be employed where it is desiredto secure even better distribution of the electrons over the innersurface of collector 92 than is possible without such a sweep means. Itis to be understood that an arrangement such as coils 94 and 95 may beemployed with other embodiments of the invention.

Modification of FIGURE 6 In FIGURE 6, we have shown a modification inwhich a very high current, high beam intensity gun is employed in whichthe electrons expand after leaving the anode land in which a magnet isemployed to cause the beam of electrons to reconverge.

Referring specifically to the drawing, the electron emissive surface isindicated by the reference numeral 105. It will be noted that thissurface is spherically concave and it will be understood that it iscoated with a suitable electron emissive material. The electron emissivesurface is supported by a chamberlike cathode structure 106 having ahollow interior for the reception of radioactive material 107 forheating the electron emissive surface 105. It is to be understood, ofcourse, that any other suitable means may be employed for heating thecathode by any source of heat which it is desired to convert intoelectricity. The cathode structure 106 is provided with a closure member108 for the insertion of the radioactive material. This closure may beof heat insulating material and where radioactive material is employed,the closure and the cathode structure 106 would be covered by materialacting as a barrier to the transmission of radioactivity. Where a sourceof heat, such as a flame, is employed, it will be understood that thecover member 108 would be omitted or would beprovided with an openingfor the reception of a burner member.

Surrounding the electron emissive surface 105 is an annular focusingelectrode 110 which has a spherically concave inner surface whichconstitutes a continuation of the spherically concave electron emissivesurface 105. This annular focusing electrode 110, which is shown asbeing at cathode potential, serves to concentrate the electrons leavingthe electron emissive surface 105.

Secured to the cathode structure 106 but spaced therefrom by aninsulating annular member 112 is an anode structure 113 comprising adisc member 114 at the lower end thereof which disc member has a passage115 therethrough, through which the electron beam passes. The opening115 is preferably slightly smaller in diameter than that of the electronemissive surface 105. Upon passing into the interior of the anodestructure 113, the electrons in the beam 117 drift apart as shown in thedrawing. In order to reconverge these electrons, a cylindrical magnet118 surrounds the upper portion of the anode structure. This magnet isprovided with a magnetic field the direction of which is parallel to theaxis of the electron beam and serves to cause the beam to reconverge inthe manner shown. The anode structure 113 has an annular flange 120 atthe upper end thereof terminating in a downwardly turned flange 121which is sealed by a suitable sealing and insulating seal 122 t-o acylindrical casing 123 constituting the collector of our device. Thischamber 123 may be formed of metal or other suitable conductivematerial. It will be, of course, understood that the chamber 123 maylikewise be formed of nonconductive material with an interior conductivecoating, as shown in lconnection with FIGURES l and 2. Secured withinthe lower por-tion of the cylindrical chamber 123 is a post-acceleratorelectrode 125 having an opening 126 therethrough, this opening beingbounded by a flanged portion surrounding the opening. As will beexplained, this post-accelerator electrode 125 is maintained at asomewhat higher potential than the anode structure 113. The electronstream, while passing through the opening 126, is thus furtheraccelerated as it is converging due to the action of magnet 118. Theelectrode 125 is provided with a lead-in terminal member 128 suitablysealed within and insulated from the wall of the cylindrical chamber123.

Supported above the post-accelerator electrode 125 is a deceleratingelectrode 130 having an aperture 131 therethrough which is concentricwith aperture 126 and slightly larger. The decelerating electrode 130 issecured to a lead-in terminal 132 which extends through the Wall ofchamber 123 and is suitably sealed and insulated therefrom. Thedecelerating electrode 130 is maintained at a lower potential than anode113 and the post-accelerator electrode 125 and serves to reduce thepositive field that would otherwise be present due vto the anode 113 andthe post-accelerator electrode 125.

Secured above the decelerating electrode 130 is a still furtherelectrode 135 which functions as a pusher electrode. This electrode hasan aperture 136 therethrough which aperture may be slightly concial withthe wider part of the aperture at the upper surface of the electrode.This aperture 136 is preferably somewhat larger than the aperture 131.The electrode 136 is secured to a lead-in terminal 138 extending throughand sealed in an insulating manner from the wall of chamber 123. Thispusher electrode 135 is connected so as to be negative with respect tothe cathode and acts to repel the electrons into the collector 123 tofacilitate the electrons moving to the interior of the cylindrical wallof chamber 123. Secured to the upper end of the collector 123 is anexhaust conduit 140 to which is connected an electronic ion pump 141.This pump includes a magnet 142 and the pump and magnet are shielded bya casing 143 of magnetic material so that the action of the beam 117 ofelectrons will not be interfered with.

A predetermined relatively high potential is maintained between theanode structure 113 and the cathode structure 106 by a suitable sourceof voltage `such as a battery 145'. This voltage may be of a magnitudefrom one to ten thousand volts. Connected in series with battery 145 isa further battery 146 to maintain the positive potential between thepost-accelerator electrode 125 and the anode structure 113, the lead-interminal 128 -of post-accelerator electrode 125 Abeing connected to thepositive terminal of battery 146, the negative terminal yof which isconnected to the positive terminal of battery 145. The deceleratingelectrode 130 is connected through lead-in terminal 132 and conductory148` to an intermediate tap 149 of battery 145. This intermediate tap149 is at a potential substantially lower than the anode potential 113and acts so that the decelerating electrode 130 is maintained at a muchlower potential than anode structure 113 and at a still lower potentialthan that at which the postaccelerator electrode 125 is maintained Thepusher electrode 135 is connected through its lead-in terminal 138` anda conductor 149 to the negative terminal of a suitable source of powersupply, such as battery 150, the positive terminal of which is connectedto the cathode structure 106. The pusher electrode is thus -maintainedat a potential negative with respect to the cathode structure, as poinedout previously.

A suitable load 151 has its upper or negative terminal connected througha conduct-or 152 to the wall of cylindrical chamber 123, which aspreviously pointed out, acts as the collector. The lower positiveterminal of resistor 151 is connected to ground at 153, this groundconnection being in turn connected to the cathode structure 106. Afurther power supply, shown in the form of a battery 154, is connectedbetween the wall of the collector 123 and the terminal 156 of the lionpump. The purpose of this power supply 154 is to provide a source ofenergy for operation of the ion pump.

Referring now to the operation of FIGURE 6, the beam of electronsproduced bythe electron emissive surface is focused lby the annularfocusing electrode 110 and passes through the aperture of anode disc114, being accelerated as they approach the anode disc. The beam ofelectrons then enters the drift chamber Within the cylindrical anodestructure 113 and due to the mutual repulsion between the electronsdiverges outwardly until it reaches the area in which the eld of magnet118 is effective. Thereafter, the beam begins to converge until itreaches a point above the aperture 126 of the postaccelerator electrode125. The distance between this point at which the beam is again fullyconverged from the point of maximum divergence of the beam 117 issubstantially equal to the distance between the point of maximumdivergence and the electron emissive surface 105.

As the beam of electrons approaches the opening 126 in thepost-accelerator electrode 125, it is further accelerated so that itenters the aperture 131 of the decelerating electrode at a relativelyhigh speed. Due to the fact that the decelerator electrode 130' ismaintained at a potential substantially lower than the potential ofanode 113 and even lower with respect to the post-accelerator electrode125, the positive field which would otherwise exist in this area isreduced so as to tend to retard or substantially prevent the return ofelectrons to the postaccelerator anode 125 and the anode 113.

The beam Iof electrons then passes through the opening 136 of the pusherelectrode 135 which, as previously pointed out, is maintained at apotential negative with respect to the cathode 105. The effect of thiselectrode is to repel the electrons so as to force them into theinterior of the collector chamber 123 ywhere they move rapidly apart.Due to the effect of the pusher electrode and to the mutual repulsion ofthe electrons, these electrons move apart and engage a major portion ofthe interior wall of the cylindrical chamber 123 above the pusherelectrode 135. These electrons, as they engage the interior of this wallare drawn off through the load 151 back to the cathode 106.

The function of the ion pump 141 is to draw off any ions that may beformed in the converter construction so as to maintain the entirestructure at a very high vacuum to an even greater extent than ispossible with the use of getter material. It is to be understood that anion pump such as ion pump 141 may be employed with any of the othermodifications which we have shown where it is desired to maintain theapparatus at a very high vacuum.

Modification of FIGURE 7 The modification of FIGURE 7 shows an expedientwhich may be employed in connection with any of the collectors. In thiscase, the collector generally is designated yby the reference numeral160. Located on the interior of the collector wall are a plurality ofprojections 161 which are spaced uniformly around the interior of thewall in a circular row. These projections act as pickup probes, tendingto attract the electrons to them and thus reducing the field gradientadjacent the aperture of lthe collector. This helps to insure collectionof the electrons on the interior wall of the collector 160 and to aid inthe movement of the electrons to the interior of the FIGURE 8 shows thechart illustrating the relationship between the percentage of maximumpossible collector current and maximum possible collector voltage. Itwill be noted that as the collector voltage is increased to its maximumvalue, the maximum possible collector current remains substantiallyconstant up to a point 165 identiiied yby the legend Maximum PowerPoint. Thereafter, as the collector voltage is increased, the collectorcurrent decreases since the value thereof is limited Iby the spacecharge. When the collector voltage reaches its maximum possible value,the current will be substantially zero. It is to be understood that thecurrent depicted is somewhat schematic and will vary with differenttypes of converter structures. Generally in all of the various versionsof our device, the current due to the load limited voltage tends toremain relatively constant until the collector voltage reaches apredetermined point at which it begins to fall `E as the collectorvoltage increases.

It will be obvious from the diagram of FIGURE S that where one desiresthe maximum power output, the load 151 should be so selected that thelsystem operates at approximately the point indicated by numeral 165. Itis at this point that the collector voltage is at the maximum pointpossible without substantial reduction in the collector current.

Summary It will he seen that We have provided a thermionic converter inwhich the collector is substantially spaced from the electron emissivesu-rface and in which it is unnecessary to employ any ionizing gases. Asa result, much higher collector voltages may be used than have hithertobeen possible. Furthermore, it is possible to obtain a relatively highdegree of efficiency.

While We have shown various methods of heating the electron emissivesurface of the cathode, it is to be understood that these have been fo-rillustrative purposes only and that the electron emissive surface may beheated by any source of heat which it is desired to convert intoelectricity.

While we have shown several types of guns for producing a stream ofelectrons, it is to be understood that other suitable types of guns maybe employed.

It is also to -be understood that while We have shown batteries as thevoltage sources, this is again merely for purposes of illustration. Inactual practice, it would usually Ibe desirable to derive voltages fromthe voltage appearing across the load and apply these voltages to thevarious electrodes .so that no exterior power source would he necessary.

It is also to be understood that various features shown specifically inconnection with one embodiment may be employed in connection with otherembodiments. Thus, the beam may be electrostatically focused, it may befocused by an electromagnet as in FIGURES 1 and 2, by a yoke type magnetas in FIGURE 3, by an electrostatic electrode such as electrode 77 ofFIGURE 4, or by an annular magnet such as magnet 118 of FIGURE 6.

Similarly, it is possible to employ a control voltage operating inconnection with a control grid as in FIG- URES 1 and 2 but such avoltage need not be employed where no control of the electron beam inthis manner is desirable.

Various expedients can be employed in vany of the modifications for morethoroughly distributing the electrons on the collector surface. Thus,sweep coils such as sweep coils 94 and 95 may be employed. Likewise, apusher electrode such as electrode 135 of FIGURE 6 may be employed.Again, the probes of FIGURE 7 may be employed in connection with any ofthe modifications. Likewise, the anode voltage may be pulsed -t-o causethe electrons to be subjected to a pumping action.

1'2 In general, while we have shown certain' specific ernbodiments ofour invention for purposes of illustration, it is to be understood thatour invention is limited solely by the scope of the appended claims.

We claim as our invention:

1. A thermionic converter for converting heat energy to electricalenergy comprising an enclosure including means for producing a beam ofelectrons including a thermionic cathode, adapted to be heated by asource of heat,

means for accelerating said beam of electrons comprising an anode havingan aperture therethrough,

and a collector having a conductive surface within said enclosure,

a source of heat for heating said cathode and of a magnitude such thatit constitutes the primary source of external energy applied to saidconverter,

means for applying a positive voltage between said anode and saidcathode to accelerate the passage of said electrons through the aperturein said anode to cause said electrons to engage the conductive surfaceof said collector,

and means operative to withdraw the electrical energy from saidgenerator resulting from the heat applied to said cathode,

said means including a utilization circuit connected between saidcollector and said cathode to withdraw the energy from the collector dueto the electrons engaging the conductive surface thereof, saidutilization circuit being free of any external electrical source ofpower.

2. A thermionic converter for converting heat energy to electricalenergy comprising an enclosure including means for producing a beam ofelectrons including a thermionic cathode adapted to be heated -by asource of heat,

and a collector having an extended conductive surface within saidenclosure which is much greater in area than the electron emissivesurface of said cathode,

a source of heat for heating said cathode and of a magnitude such thatit constitutes the primary source of external energy applied to saidconverter,

means for causing said beam of electrons to engage said extendedconductive surface of said collector,

and means operative to withdraw the electrical energy from saidgenerator resulting from the heat applied to said cathode,

said means 'including a utilization circuit connected between saidcollector and said cathode to withdraw the energy from the collector dueto the electrons being repelled from each other as they approach saidcollector and engage the extended conductive surface thereof, saidutilization circuit being free of any external electrical source ofpower of the same order of 1magnitude of energy as that of said sourceo-f eat.

3. A thermionic converter for converting heat energy to electricalenergy comprising an enclosure including means for producing a beam ofelectrons including a thermionic cathode adapted to be heated by asource of heat,

means for accelerating said beam of electrons,

and a collector hav-ing an extended conductive surface within saidenclosure which is much greater in area than the electron emissivesurface of said cathode,

a source of heat for heating said cathode and of a magnitude such thatit constitutes the primary source of external energy applied t-o saidconverter,

means for applying a positive voltage between said accelerating meansand said cathode to accelerate the passage of said electrons to causesaid beam of electrons to engage said extended conductive sur- -face ofsaid collector,

and means operative to withdraw the electrical energy from saidgenerator resulting from the heat applied to said cathode,

said means including a utilization circuit 4connected between saidcollector and said cathode to withdraw the energy from the collector dueto the electrons being repelled from each other as they approach saidcollector and engage the extended conductive surface thereof, saidutilizati-on circuit being free of any external electrical source ofpower of the same order of magnitude of energy as that of said source ofheat.

4. A thermionic converter for converting heat energy to electricalenergy comprising an enclosure including means for producing a beam `ofelectrons including a thermionic cathode adapted to be heated by asource of heat,

and a hollow collector having a conductive surface within saidenclosure,

a source of heat for heating said cathode and of a magnitude such thatit constitutes the primary source of external energy applied to saidconverter,

means for causing said beam of electrons to enter into said hollowcollector,

and means operative to withdraw the electrical energy from saidgenerator resulting from the heat applied to said cathode,

said means including a utilization circuit connected between saidcollector and said cathode to withdraw the energy from the collector dueto the electrons being repelled from each other within said collectorand engaging the conductive surface thereof, said utilization circuitbeing `free of any external electrical source of power.

5. A thermionic converter for converting heat energy to electricalenergy comprising an enclosure including means for producing a beam ofelectrons including a thermionic cathode adapted to be heated by asource of heat,

means for accelerating said beam of electrons,

and a hollow collector havin-g a conductive surface within saidenclosure,

a source of heat for heating said cathode and of a magnitude such thatit constitutes the primary source of external energy applied to saidconverter,

means for applying a positive voltage between said accelerating meansand said cathode to accelerate the passage of said electrons to tend tocause said electrons to enter said hollow collector,

and means operative to withdraw the electrical energy from saidconverter resulting from the heat applied to said cathode,

said means including a utilization circuit connected between saidcollector and said cathode to withdraw the energy from the collector dueto the electrons being repelled from each other with said collector andengaging the conductive surface thereof, said utilization circuit beingfree of any external electrical source of power of the same order ofmagnitude as that of said source of heat.

6. The thermionic converter of claim 2 in which electromagnetic meansare employed for controlling and directing the beam of electrons.

7. The thermionic converter of claim 2 in which a permanent magnet isemployed for controlling and directing the beam of electrons.

8. The thermionic converter of claim 2 in which an electrostaticfocusing electrode is employed for focusing the beam of electrons.

9. The thermionic converter of claim 2 in which beam sweeping means areemployed for dispersing the beam of electrons on the conductive surfaceof the collector.

10. The thermionic converter of claim 2 in which a control grid isprovided to regulate the amount of beam current or to modulate theoutput voltage.

11. The thermionic converter of claim 1 yin which the interior of thecollect-or has at least one pickup probe therein to facilitatecollection of electrons.

12. The thermionic converter of claim 1 in which the electrons areallowed to diverge and are then reconverged by suitable focusing meansso that they are substantially fully converged as they enter thecollector region.

13. The thermionic converter of claim 5 in which an electrode isdisposed adjacent to the entrance to the collector and is maintained ata volt-age negative with respect to the cathode to alter the positiveeld produced by the accelerating means and hence to minimize thetendency of the electrons to return to the accelerating means.

14. The thermionic converter of claim 5 in which the cathode is designedto receive a burner for heating the cathode emissive surface thereof.

. 15. The thermionic converter of claim 5 in which the cathode isdesigned to retain radioactive material in heat transfer relation withthe electron emissive surface of the cathode.

16. The thermionic converter of claim 5 in which the cathode is designedto have a hot fluid circulated in heat transfer relation with theelectron emissive surface of the cathode.

17. The thermionic converter of claim 3 in which the accelerating meansis an anode having an aperture therethrough through which the beampasses.

18. The thermionic converter of claim 5 in which the accelerating meansis an anode and in which said anode and the hollow collector havealigned apertures through which the beam of electrons passes to enterthe interior of said collector.

19. The thermionic converter of claim 18 in which there is at least onefurther electrode maintained at a diiferent potential than said anodefor affecting the beam of electrons in a desired manner.

References Cited by the Examiner UNITED STATES PATENTS 2,907,908 10/1959 Bryan S13-84 2,915,652 12/1959 Hatsopulos et al. 310-4 2,953,706 9/1960 Gallet 310-4 JOHN F. COUCH, Primary Examiner. LLOYD MCCOLLUM,Examiner.

W. H. BEHA, Assistant Examiner.

1. A THERMIONIC CONVERTER FOR CONVERTING HEAT ENERGY TO ELECTRICALENERGY COMPRISING AN ENCLOSURE INCLUDING MEANS FOR PRODUCING A BEAM OFELECTRONS INCLUDING A THERMIONIC CATHODE, ADAPTED TO BE HEATED BY ASOURCE OF HEAT, MEANS FOR ACCELERATING SAID BEAM OF ELECTRONS COMPRISINGAN ANODE HAVING AN APERTURE THERETHROUGH, AND A COLLECTOR HAVING ACONDUCTIVE SURFACE WITHIN SAID ENCLOSURE, A SOURCE OF HEAT FOR HEATINGSAID CATHODE AND OF A MAGNITUDE SUCH THAT IT CONSTITUTES THE PRIMARYSOURCE OF EXTERNAL ENERGY APPLIED TO SAID CONVERTER, MEANS FOR APPLYINGA POSITIVE VOLTAGE BETWEEN SAID ANODE AND SAID CATHODE TO ACCELERATE THEPASSAGE OF SAID ELECTRONS THROUGH THE APERTURE IN SAID ANODE TO CAUSESAID ELECTRONS TO ENGAGE THE CONDUCTIVE SURFACE OF SAID COLLECTOR, ANDMEANS OPERATIVE TO WITHDRAW THE ELECTRICAL ENERGY FROM SAID GENERATORRESULTING FROM THE HEAT APPLIED TO SAID CATHODE, SAID MEANS INCLUDING AUTILIZATION CIRCUIT CONNECTED BETWEEN SAID COLLECTOR AND SAID CATHODE TOWITHDRAW THE ENERGY FROM THE COLLECTOR DUE TO THE ELECTRONS ENGAGING THECONDUCTIVE SURFACE THEREOF, SAID UTILIZATION CIRCUIT BEING FREE OF ANYEXTERNAL ELECTRICAL SOURCE OF POWER.